A large truck, such as a dump truck, has a two-shaft structure for supporting the rear wheels in order to evenly support a load, particularly while traveling on a rough unpaved road.
A rear-wheel suspension system of a large truck, which has a two-shaft structure for supporting the rear wheels, includes a pair of rubber springs, which are mounted to a front rear-wheel axle and a rear rear-wheel axle, and a leaf spring, which extends in the forward-and-backward direction such that two opposite ends thereof are connected to the rubber springs.
A trunnion base, which includes a trunnion shaft, is provided at the middle in the longitudinal direction of the leaf spring. The trunnion base is coupled to a vehicle body frame, and a U-bolt saddle (an under saddle or a lower saddle) is rotatably coupled to the trunnion shaft and is coupled to the middle portion of the leaf spring, together with a spring bracket (an upper saddle), by fastening a U-bolt and a nut, in order to fixedly support the middle portion of the leaf spring.
The leaf spring may be constituted by multiple steel plates, or may alternatively be embodied as a composite leaf spring, which is formed in a unitary body containing glass fiber or carbon fiber. The leaf spring, which is constituted by multiple steel plates, is advantageous in terms of high durability for a given price, and the composite leaf spring is advantageous in terms of reduction in weight and improvement of fuel efficiency.
The composite leaf spring, which is formed of a mixture of glass fiber and resin, is vulnerable to friction and thus has a shortcoming of low abrasion resistance. Therefore, the composite leaf spring, which is vulnerable to friction, cannot be manufactured using multiple plates like a steel leaf spring, but is formed in a unitary body.
In particular, if a portion of the composite leaf spring to which the U-bolt is mounted is excessively worn, the axial force, i.e. the clamping force, of the U-bolt greatly decreases. As the axial force of the U-bolt excessively decreases, a larger torsional force is applied to the composite leaf spring, and thus, the durability of the composite leaf spring greatly decreases, which entails the likelihood of an accident.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.